This invention relates to a multi-needle sewing machine and, more particularly, this invention enables a multi-needle sewing machine to sew parallel curved stitch lines by controlling the feeding of each needle thread in proportion to each radius of curvature of the stitch line.
Generally, a take-up lever is used for controlling the supply of a needle thread. In some cases, extra thread feeding controllers are equipped such that the needle thread is fed positively from a thread spool.
Referring to FIG. 5, where two stitch lines 2, 3 are to be positioned with a predetermined margin from the end of the workpiece, if the thread feeding rates for both stitch lines 2, 3 are adjusted for the stitch line 2, the stitch line 3 tends to be stitched in a looser condition than the stitch line 2 because the radius r.sub.2 is smaller than the radius rl.
On the other hand, if the thread feeding rates for both stitch lines 2, 3 are adjusted for the stitch line 3, the stitch line 2 tends to be stitched in a tensioned condition and the workpiece shrinks at the periphery. Thus, it is very difficult to make well-balanced and technically fine stitch lines.